Adjustable thermostat switch



May 27, 1947. 'J, L SC WARTZ 2,421,292

ADJUSTABLE THERMOSTAT SWITCH Filed April 26, 1946 l N V E N T O R Ja/m/lza/v/z/w Jean/4H 72 ZZW ATTORNEYS Patented May 27, 1947 2,421,292ADJUSTABLE THERMOSTAT swrron John Leonard Schwartz, Philadelphia, Pa.,as-

signor to Clarence A. Rossman, J. Leonard Schwartz, and Hugo Engelhardt,a. copartnership doing business as Ihe Philadelphia Thermometer Company,Philadelphia, Pa.

Application April 26, 1946, Serial No. 665,164

Claims.

This invention relates to adjustable thermostats, and particularly tothe increase in accuracy thereof.

In an application Serial Number 611,819, filed August 21, 1945, Idisclosed an improved adjustable thermostat of high efliciency andutility. It is a feature of that application to provide a double boredthermometer tube in one bore of which an adjustable contact member inthe form of a wire electrode was slidably mounted to establish one sideof the line of the circuit to be controlled, and the other bore containsa permanent contactor completing the circuit through the instrument. Ithas been found that sometimes certain features of inaccuracy attached toapparently identical thermostats made according to that and otherdisclosures, which it is the principal object of this invention toobviate.

Among the objects of the invention are: to provide an improvedthermostat; to provide a thermostat in which 'a series of substantiallyidentical instruments will have predetermined substantially identicalhigh degrees oi accuracy; and to provide other objects and advantages aswill become more apparent as the description proceeds.

In the accompanying drawings forming part of this disclosure:

Fig. 1 represents a longitudinal section of the thermostat of saidapplication as modified by the invention herein.

Fig. 2 represents a fragmentary section on an enlarged scale through thethermostat of Fig. 1 with a made contact relation between a wireelectrode and the end of a mercury column.

Fig. 2A represents a fragmentary section simi lar to part of Fig. 2 witha broken contact relation between a wire electrode and the end of themercury column.

Fig. 3 represents a transverse section taken through the thermostat ofFig. 1 on line 3-4 of Fig. 2.

Fig. 4 represents a fragmentary section through a modified form of abarrel of an adjustable thermostat, showing a modified form of anadjustable electrode wire therein.

Fig. 5 represents a transverse section through the barrel shown in Fig.4, on line 5-5 thereof The thermostat shown in Fig. 1, as purelyillustrative of an application of the invention, comprises a barrelordouble bored shank I0 containing the two capillary bores, respectivelythe inactive bore II, and the active bore I2. The

latter communicates directly with the mercury II in the bulb ll. Bothbores preferably communicate with the enlarged upper chamber and mercuryreservoir i5 containing the actuating mechanism formed of the supportingpanel l8 seated on a median partition i9, and on which panel isrotatably journalled a threaded shank I'I, carrying the armature [8, bythe rotation of which a travelling electrode wire 20 is suitably causedto be vertically adjusted in the bore l2. Rotation is effected by therotatable annular magnet 2|. A suitable connection is establishedbetween the adjustable wire electrode 20 and one terminal 1 of thethermostat, and a wire 22 extends from the other terminal 8 into thebore H from which to complete the circuit. A transverse embeddedelectrode wire 0r connector 23 extends from the inactive bore II to theactive bore i2. Any of the modified forms of thermostat shown in thatapplication may equally well be used.

It has been discovered that with apparently identical processing, thedegrees of accuracy between apparently identical instruments weresometimes measurably diiferent, and this also pertains to the resultsfrom other types of thermostats, as shown, for instance, in U. S. PatentNo. 2,108,338, to Juchheim, granted February 15, 1938, with a barrelhaving a single bore and an axially movable wire in that bore for themaking and breaking of th circuit through the mercury. Afterconsiderable research, it has been discovered that the reason for thefluctuations or variations in responsiveness arises from the differencesin the location of the contact-making end of the wire electrode relativeto the walls of the bore. It has been found that there are two untowardhappenings when the free end of the wire electrode is out of thesubstantially coaxial center of the bore and in contact or substantialcontact with the walls of the bore. One unfortuitious happening is themore or less permanent lodgement of mercury between the electrode andbore wall by a species oi. capillarity manifested usually as anupswelling bulge asymmetrical of the miniscus of the mercury. This is avariable happening as it can sometimes be dislodged by shock orvibration and sometimes it cannot, and as it distorts the end of thecolumn of mercury in the bore, its adverse effects on readings can beimagined. The other undesirable characteristic attaching to asymmetricaldisposition of the free end of the wire electrode in the bore is becauseof the fact that the bore is a capillary bore, within which the end ofthe mercury forms a miniscus, and after substantial stabilization for acertain time interval the mercury seemingly becomes more or lessattached to the 3 walls of the bore, especially where the convex surfacethereof intersects and contacts the bore wall. Pursuant to thiseflective relative attachment, if this is the term for the phenomenon,slight changes in the temperature incident upon the mercury iii in thebulb l4, accompanied by a slight change in the volume of mercuryinstantaneously present in the bore l2 and bulb I4, is manifestedinitially by a mere change in the profile of the miniscus. This profilechange depends for its sense upon the direction or sense of temperaturechange, and the curvature, i. e., the relative convexity or concavity ofthe miniscus, changes in the center without actual movement at the edgethereof in contact with the bore walls. Of course, continuance ofchanged temperature causes actual movement of the entire miniscusaxially of the bore, but for sensitive control purposes, the first faintbreathing of the miniscus is the only activity by which to securecontrol functions. It will be readily seen that under such conditions ofbreathing without axial shift of the entire miniscus, that thesensitivity of the thermostat would vary as a function of the distancethe wire electrode end is from the axial center of the bore and,therefore, of the miniscus. It is, therefore, the primary object of thisinvention to cause the electrode wire to be centered in all of itspositions in the bore, whether elevated or depressed therein, while atthe same time avoiding any stoppage in the bore which might act as atrap to mercury.

In carrying out the invention in an illustrative form, the wireelectrode 20 is formed into a sliver point as at 24. Close to the point,say, illustratively, from 3 to therefrom, or thereabouts, a rounded bendor crimp 25 is made in the wire, of such external extent radially of thebore and of the axis of the wire, as to enable guided bearing on a wallof the bore. At a short axial distance therefrom, say, illustratively atabout V preferably in the same plane containing the wire 20 and thecrimp 25, a second crimp or bend 26 is formed, preferably extendingradially from the wire in a direction opposite to crimp 25, and of suchexternal extent radially of the bore and of the axis of the wire as toenable guided bearing on the wall of the bore opposite to that surfacejuxtaposed to crimp 25. The wire electrode, preferably formed oftungsten or the like may be given the crimps in any desired way, butillustratively a pair of cooperating complemental dies are formed to givthe wire the slight indentations or crimps shown in such enlarged scalein Figs. 2 and 3. With the wire electrode 20 slid endwise into the borel2, the point 24 thereof will be held in centered relation by theoppositely disposed crimps or bends 25 and 28, with the range ofpossible deviations of the point from the exact axis outlining averysmall area. It will be observed in this connection that movement in theplane of the crimps diametrical of the bore is limited by the clearancebetween the outer edges of the crimps and the surface of the bore.Movement bodily in a line transverse to the plane of the wire and crimpsis also limited by this same clearance projected transversely againstthe bore surface. At the same time, there is preferably such relativelyloose engagement as to minimize adverse frictional eifects.

With the wire electrode 20 disposed in the bore II with the point 24thereof centered, and with the centered relation maintaining duringmovements of the electrode axially of the bore, it will be observed thatthe expanded mercury Hi from th bulb l4 rising in the bore l2, with theupper least to establish contact with th'e substantial,

center of the miniscus. As shown in F18. 2, the center of the miniscusis axially appreciably closer to the point 24 than the edge 24 of theminiscus where it contacts the surface of the bore I2. The contactcloses the circuit throughth'e instrument and through any desiredamplifying or relay system, to actuate any desired control orindication, but as this latter forms no part of the present invention nopart of the control circuit, as such, is disclosed.

After the circuit has been made by contact of the substantial center ofthe miniscus with the end 24 of the electrode 24, in due course therewilldevelop a slight change in the temperature incident upon the bulbI4, which will manifest itself in its initial, almost its incipientstage. as a downward breathing" of the miniscus. By this preliminaryresponsiveness, without any relative movement of the edge 20 of theminiscus and the surface of the bore i2, which it intersects, theconvexity of the miniscus decreases and it becomes relatively moreflattened, as shown in Fig. 2A. This withdraws the center of theminiscus from its circuit-making contact with the point 24 and thecircuit is broken. Thereafter, bythe operations of the device with whichit is associated or the like, the temperature incident upon the bulb i4may increase. This again cause -elongation of the miniscus until thesubstantial thereof again contacts the point 24 of the electrade 20without disturbing the peripheral line 29 of the edge of the miniscus,and the circuit is again made.

It will be apparent that as the point 24 of an uncrimped wire departsfrom a concentric relation in the bore and moves closer to the surfaceof the bore I2, and this is the actual result or previous forms ofelectrodes used in any form of thermostat known to me, with the degreeof departure from the axial center being unpredictable, the sensitivityof the instrument decreases. The particular degree of decrease'ofsensitivity varies between supposedly identical instruments at datumtemperatures, and may also vary between supposedly identical instrumentswith changes of setting, and it is, therefore, highly desirable that thepoint 24 be accurately centered at all times and this is accomplishedwith the formation of the guide surfaces 25 and 24 of Fig. 2. In thisconnection, it will be seen that for one reason or another it is quitepossible for the mercury II to rise in the bore 12 or otherwise to ill]the bore (as from the reservoir formed in the enlarged chamber I5),until the mercury has immersed the crimps 2| or 24. It is a feature ofgreat importance that even such immersion has no mercury-trappingresults, as the crimp is formed in the body of the wire only, and asthis is of extreme thinness, the tendency of mercury globules to engagebetween the wall of the bore I2 and one or the other of the crimps 2! or24 is so minimized as to constitute no particular hazard. This is incontrast to any separate non-integral wire guides which might beattached to the wire, which would inevitably present such crosssectional area as either to form an actual valve or trap of more or lesspermanency for mercury disposed above it, or would manifest suchtrapping tendency as to effectively trap varying quantities at varyingtimes with a consequent upset of the accuracy of the instrument.

It has been mentioned that the invention is of value in any form ofthermostat and the only limitation is that the wire electrode bedisposed in a capillary bore of an instrument and that it be movabletherein axially of the bore, and that mercury be arranged to rise andfall in the bore relative to the end of the wire as an incident of somechange of condition effective to move the mercury. Thus, in Fig. 4 thereis disclosed a fragmentary section of the barrel of the thermostatshown, for instance, in said U. S. Patent No. 2,108,338. The barrel,illustratively designated as 28, has a capillary bore 30, in whichmercury l3, having a miniscus 21, is disposed. The electrode wire 3| hasa splinter point 32, for contacting the mercm, and may either have thesame crimps as are shown in Fig. 2, or a slightly modified form ofcrimps by which the lowermost crimp 33, adjacent to the point 32, leads,preferably directly across the line of the wire to the complementalcrimp 34, so that adjacent to the point 32 the wire is guided on bothsides of the center. If desired, the crimps 33 and 3|, instead 0! beingcomplementally continuous, may be axially spaced for a slight distanceto reduce bending of the wire and to reduce the axial proximity of thecrimps to each other to reduce any tendency such proximity mightengender to trap or hold mercury after an immersion therein. A thirdcrimp 35 may be formed in the wire 3| in axially slightly spacedrelation to the pair of crimps 33 and 34, as a stabilizing guide crimp.It will be seen that from the standpoint of positive guide, the crimparrangement of Fig. 4 offers more lateral bearing area and guidingfunction than the two oppositely disposed crimps of Fig. 2. On the otherhand, the stability and positive guidance from the pair of axiallyspaced crimps of Fig. 2 have been found for all practical purposes to besatisfactory.

The cheapness, eiiiciency and positive operation of the invention andthe enhanced accuracy of the system will be clear.

Having thus described my invention, I claim:

1. A thermostat comprising a barrel having a capillary bore, mercury inthe bore, a movable electrode wire disposed in the bore. said wirehaving a plurality of lateral bends in such relative 6 angularity as toguide the wire in the bore to maintain its substantial concentricitytherein.

2. A thermostat comprising a barrel having a capillary bore, mercury inthe bore, a movable electrode wire disposed in the bore, said wirehaving lateral bends in axially spaced relation and anguiarly so spacedas to guide the wire in the bore to maintain its substantialconcentricity therein.

3. A thermostat comprising a barrel having a capillary bore, mercury inthe bore. a movable electrode wire disposed in the bore, said wirehaving lateral bends in axially and angularly spaced relation to guidethe wire in the bore to maintain its substantial concentricity therein,said bends being in a common plane containing the wire.

4. A thermostat comprising a barrel having a capillary bore, mercury inthe bore, a movable electrode wire disposed in the bore, said wirehaving lateral bends in axially spaced relation to guide the wire in thebore to maintain its substantial concentricity therein, said bends beingrespectively oppositely projected out of the line of the wire.

5. A thermostat comprising a barrel having a capillary bore, mercury inthe bore, a movable electrode wire disposed in the bore, said wirehaving lateral bends in axially spaced relation to guide the wire in thebore to maintain its substantial concentricity therein, said bends beingrespectively oppositely projected out of the line of the wire and lyingin acornmon plane with the wire.

JOHN LEONARD SCHWARTZ.

REFERENCES CITED The iollowing references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,108,338 Juchheim Feb. 15, 19382,087,150 Hieber et al July 13, 1937 2,259,661 Pollard Oct. 21, 1941

